Process for the manufacture of zinc



June-13, 1944. H. WOLF 2,351,383

. PROCESS FOR THE MANUFACTURE OF ZINC Filed June 21, 1938 2 Sheets-Sheet 1 o o o Hermann We)? Erna Kus:

Hans Hahn /NENTOR6 Frzz Jzfdeazed THE/R HTTOR/VEV6 Patented June 13, 1944 rnocass FOR THE MANUFACTURE OF ZINC Hermann Wolf, Ernst Kuss, Hans Hohn, and Fritz Stietzel, Duisburg, Germany; vested in the Alien Property Custodian Application June 21, 1938, Serial No. 214,954

In Germany June 21, 1937 8 Claims.

son of the strongly electro-negative character of zinc, the zinc has a marked tendency to re-dissolve in the electrolyte. This tendency is greatly augmented when the zinc deposits irregularly to form warts and buds on the cathode since there occurs at these irregularities a lowering of the hydrogen overvoltage with a resultant corrosion of the cathode. It is, therefore, necessary to interrupt the electrolysis when the cathode, by reason of the formation of such irregularities, reaches a certain size.

' It is quite universally the practice to deposit the zinc from sulfate solutions from which any chlorine ions should be excluded. While the electrolysis of zinc chloride solutions is theoretically superior to the electrolysis of sulfate solutions because of the possibility of simultaneously obtaining chlorine, this theoretical superiority is difficult of realization in practice due to the yield diminishing corrosion to which the cathode is exposed by virtue of the presence of dissolved chlorine in the electrolyte. It has been considered necessary in order to avoid .this corrosion as far as possible, to employ a diaphragm to separate the anode from the cathode. This of itself adds to the expense of the process as does the time which must be spent in attending to the diaphragm. Furthermore an appreciable amount of voltage is absorbed by the diaphragm, making its use further objectionable for this reason. 'When all these factors are added 'to the further factor which requires the use of extremely pure electrolytes in order to obtain reasonable-current .efliciencies, it will be appreciated that the electrolytic recovery of zinc presents very serious obstacles to its practical adoption.

It has now been found that most vo'f the disadvantages which have heretofore manifested themselves in the electrolytic recovery of zinc may be overcome by the utilization of a mercury cathode for the electrolysis while operating at elevated temperatures and while observing certain precautions in separating the zinc from the mercury cathode for reuse of the mercurydn the process. There have been some proposals in the posals it was suggested that the zinc amalgam obtained be immediately subjected to distillation, In certain cases, however, it was suggested that the zinc amalgam produced in the original electrolytic step be used as an anode in a subsequent step, the zinc being dissolved from the anode and being re-deposited on a solid cathode. The employment of mercury as a cathode has certain disadvantages which were not overcome in the prior processes. Thus mercury cathodes, when subjected to the action of an electric current, have a tendency to pulsate whereby furrows and elevations are formed in the surface of the mercury which either lead to short circuits with the anode or at least make it impossible to space the anode and cathode a short distance apart to insure' a working at relatively low bath voltages. Furthermore amalgamation between the mercury and the deposited metal often does not take place properly, the zinc frequently forming as a very reactive gray mud or slime on the surface of the mercury whereby the cell becomes covered with this mud or slime and the current efliciency decreases. The mud operates also to develop hydrogen and in addition cannot be "worked up into pure zinc. The mud also effects a clogging of pipes and pumps necessary in a continuous process, thereby preventing a continuous and automatic operation.

On the other hand there are particular advantages which are offered by the'use of a mercury cathode on which attention hasnot been particularly focused up to the present time and which recommendthe use of a mercury cathode providing of course that the disadvantages previously mentioned can be overcome. 'For instance the amalgams have for the same current efliciency an essentially smaller surface area than solid cathodes and for this reason alone the tendency for the deposited metal to re-dissolve is lessened. The amalgams moreover behave quite'generally against corroding electrolyte constituents in a nobler manner than metallic zinc and therefore permit electrolysis of zinc chloride solutions without the utilization of a diaphragm. There is, moreover, no tendency for couples to be formed in the amalgams so that a far-reaching purification of the electrolyte which is necessary with solid anodes in order to prevent formation of such couples with resultant corrosion is not required. There is in addition no necessity to add special preparations such as colloids and the like to the electrolyte. Finally inasmuch as the amal- 'gamsare liquid, their preparation and working up can be effected in a completely continuous and automatic manner. In spite of these advantages all processes suggested up to the present time for obtaining zinc by use of mercury cathodes have been technically unsuccessful probably because steps were not taken to overcome the disadvantag'es mentioned above as well as certain difllculties which make their presence felt in the working up of the amalgam.

It is an object of the present invention to provide a process for the deposition of zinc from zinc containing lyes which is free from the dinlculties which previously were encountered in the electrolytic recovery of zinc from zinc-containing solutions.

It is a further object of the present invention to electrolytically deposit zinc from zinc-containing solutions while employing a mercury cathode and while insuring that the cathode may be spaced a short distance from the anode without the danger of the formation of short circuits arising.

It is a further object of the invention to electrolytically recover zinc from zinc-containing solutions by means of a cell having a mercury cathode while operating at elevated temperatures.

A further object of the invention comprises the electrolytic deposition of zinc with a mercury cathode while circulating the cathode and the electrolyte.

A further object of the invention involves the provision of steps to preclude contact of atmospheric oxygen with the amalgam formed in the electrolysis during the working up of the amalgam.

It is a further object of the invention to facilitate, separation of the zinc from the amalgam by mechanically concentrating the amalgam prior to the isolation of the zinc from the mer- A further object of the invention comprises a a two-stage distillation of the amalgam, the first stage being conducted under reduced pressure.

It is a further object of the invention to provide a process for recovering zinc from chlorinecontaining solutions without'the use of a diaphragm.

It is a further object of the inventionto provide a process for electrolytically recovering substantially pure zinc from zinc-containing solutions while realizing a high current efllciency.

A further object of the invention involves the apparatus for carrying out the electrolytic process.

Other objects will be apparent from the following detailed description.

As previously stated, we have now found that it is technically possible to take advantage of the possibilities of a mercury cathode in producing zinc from zinc-containing lyes by taking certain precautions during the electrolytic process and during the decomposition of the amalgam into zinc and mercury. These precautions in volve, first, the use of elevated temperatures, preferably from 55 C. to the B. P. for the electrolysis of the zinc-containing solutions. By-

working at these higher temperatures, the tensiassures ency of the mercury to pulsate is avoided and the formation of the zinc in the form of'a mud is precluded even at high current densities. This permits circulation of the cathode without disturbance to the mechanical equipment. Furthermore the anode and cathode can be spaced within a few millimeters of each other without dangers of short circuiting, a considerable sav- 1 ing in current thereby being realized. 7

. Generally elevated temperatures are avoided in the electrolysis oi zinc solutions for the reason that they lead to a decrease in current efllciency by lowering the hydrogen overvoltage and by increasing the rate of chemical corrosion (see heading (1). page 314 of "Applied Electro-Chemistry" by Allmand and Ellingham, 2nd edition).

It is, therefore. surprising that in the process developed by us the utilization of high tempera-.

tures contrary to leading to the objections noted in the above treatise, operate to facilitate the carrying out Of the electrolytic process.

The second precaution involves the production of an amalgam having a good flowability. By an amalgam with a good flowability is understood an amalgam which resembles pure'mercury in its flowability, does not contain any solid amalgam particles and does not show any tendency to separate into more or less thick amalgam pulps. The good flowabilit of the zinc amalgam is a function of the temperature and the amalgam concentration so that these 2 factors must be most carefully supervised. The following examples serve'to further illustrate what is meant by an amalgam with a good flowability:

Amalgams with 2% Zn at 25 Amalgams with 4% Zn at 70 Amalgams with 5% Zn at 80 If these limits be surpassed the amalgams, it is true, are still liquid. They will not, however, flow well in the sense oi the present process as they are no longer quite homogeneous and tend to eliminate crusts and pulpy products.

The consistency of the amalgams at a specifled zinc content and a constant temperature may fluctuate a good deal. Dry, we11 flowable amalgams, especially when in movement, are slowly permeated by thick, spongy deposits or 'dross, whichdestroy their flowability and clog the pipes and apparatus in time. This can be avoided by carefully excluding oxygen of the air from contact with the amalgam, for instance by employing closed apparatus and conduits or by causing an inert gas to flow over the surface of the amalgam. It is also possible to operate with great advantage by covering the amalgam in I the troughs or channels provided for its conduction and also in other apparatus parts with a weak acid, for instance very dilute hydrochloric acid.

' In this case the channels may be subdivided by mercury cathode. It has been discovered that with the mercury cathodes lower current emciencies are obtained when the cathodes are in motion than when the cathodes are at rest, the decrease in efliciency being the greater, the greater themovement of the mercury. In order to obtain good current efllciences, the current assnsas to guarantee a uniform concentration of. the

amalgam in continuous operation and to avoid the occurrence of isolated deposits of higher zinc concentration. This movement may be eifected by forming the mercury cathode in horizontal streams or rows which have a uniform fall or gradient of 1 to 2 millimeters per meter.

We have found that especially satisfactory current efficiencies can be obtained if the enrichment of the zinc in the amalgam be effected in steps in various cells operating in series rather than in a single cell. For instance the process may be operated in such a manner that the amalgam formed in each cell is led in a cycle, a certain part of the amalgam being branched of! from each cell and led to'the next succeeding cell. Thequantity of amalgam branched 01! from each cell should as a rule be high enough tocorrespond to the quantity of zinc simultaneously precipitated by the electric current. The amalgam concentration prevailing in each cell can be regulated by a temporary throttling of the amalgam supply or by adding fresh mercury. It is preferable to operate so that in each succeeding cell the amalgam concentration increases by about 1%. For the conduction of the amalgam and for effecting the necessary current interruption it is advantageous to arrange the related cells one over the other so that the amalgam flows without the aid of pumps or other conveying devices and merely under the influence of gravity from one cell to the other. 1

It is advisable to carry out the electrolysis with lyes rich in zinc, for instance with 100 grams of zinc per liter. It is a characteristic of the process, however, that it is also suitable for electrolysis of lyes poor in zinc. The process offers for example the possibility of working up lyes obtained by a chlorinating roasting of pyrites in a simple manner to zinc and chlorine. As is known, the main elements in such lyes are copper and zinc combined with lead, nickel, cobalt, cadmium, gold, silver and other impurities. The individual elements are eliminated in known manner one after the other by suitable operations until there remain only zinc dissolved as zinc chloride in comparatively slight concentration together with alkaline earth chlorides and large quantities of sodium chloride and different heavy metal impurities.

cipitating the zinc as oxide, dissolving the oxide in sulphuric acid and after a high purlfication, electrolyzing the resultant sulfate.

other metals present. It is not necessary to completely purify the lyes since purification need In former a practice lyes of this type were treated by preonly go so faras is commensurate with the desired degree of purity of the depoflted zinc. Of

the impurities present the copper, lead and cadmium go quantitatively into the zinc amalgam upon electrolysis, nickel only partly and cobalt hardly at all. Asno couples are formed, the current. efficiencies are not influenced to any particular extent. The presence of magnesium and alkaline earths in the electrolytes is of no importance. The presence of large amounts of sodium chloride is, however, quite desirable. Contrary to the electrolysis of the sulfate solutions in which traces of chlorine in the electrolyte cause a strong corrosion of the anodes, the electrolysis of zinc chloride solutions with mercury cathodes and anodes stable to chlorine is not aifected at all by large amounts of sulfate. The chlorine developed at the anode has the usual purity and can be collected dried densifled in the usual manner. a

The current eiliciencies obtainable with mercury cathodes decrease after the removal of zinc from the lyes has advanced to a certain stage. Accordingly, therefore, the electrolysis is discontinued when the zinc content of theelectrolyte reaches about 15 to 20 grams per liter. Thelye is then treated with lime to precipitate zinc hydroxide which is recovered and :lsfid for the removal of iron from theinitial yes.

It is believed pertinent to note that the amalgam cathodes are not-insensitive to the im- I impurities are removed quantitatively from the.

electrolyte. This can be accomplished in a known manner by precipitating the ferric iron present in the electrolyte as ferric hydroxide. If necessary, in order to accomplish this purpose,

iron may be separately added to the electrolyte.

Similarly the effect of very small quantities of arsenicor antimony compounds can be minimized or avoided by adding small quantities of mineral acids. If this method be resorted. to, it is preferable not to exceed a certain acidity such as about pH=1.

A further precaution which must beobserved deals with the distillation of the amalgam by which the zinc is recovered in pure form and the mercury regenerated for further use. It is of decisive importance that this distillation be effected with the best possible utilization of heat, with cheap heat sources, without loss of mercury and as continuously as is possible. The furnace material must be resistant to attack by fused high percentage amalgam and pure zinc respectively. The mercury must be practically completely removed from the zinc. This require- .ment can be satisfied only by the employment of but are quickly destroyed by high percentage. hot

amalgams, i. e. metallic materials. The zinc is and Either the materials that come into thereby contaminated to a non-desirable extent. The distillation apparatus utilized up to the present time are such that a pure zinc and es- 'pecially a zinc practically free from mercury cannot be obtained in a technically satisfactory manner.

We have now ascertained that the main quani h second of which the ercu still resent n t e m W p .slightly violent distillation of the zinc is eflected.

Furthermore it is advisable to provide the melt is completely eliminated in a further distillation apparatus operated at essentially higher temperatures. The distillation apparatus for the first step preferably has metallic heat conducting parts which are provided with a suitable protective coating. It is advisable in operating these apparatusto supply heat externally and to distil under strongly reduced pressure. As the protective coating there may be used enamel since the distillation temperatures under reduced pressure lie below the temperatures destructive of enamel. While the amalgam is still comparatively liquid, that is while it contains only up to about of zinc, said protective layer may be omitted and there may be employed as the furnace material either cast iron, weldable iron or thermosilide (an alloy of iron and silicon). The external heating of the distillation apparatus may be advantageously effected by mercury vapor which either comes directly from a mercury boiler and is reintroduced into the boiler without a pump, or by the exhaust steam of mergas or any other suitable and cheap source of heat. In this distillation step there may be employed continuous working thin layer evaporators or circulation evaporators of suitable construction which are arranged in series and which operate at different working temperatures.

These temperatures increase from chamber to chamber with increasing amalgam content-and may. be lower the better -the vacuum and the wider the pipes from the distillation chamber to the condensation plant. The temperature of each individual unit must not exceed the melting point of the amalgam treated therein. This result can be secured by suitable reduction of pressure and by a properly selected speed of throughput. The size of the individual units decreases considerably with increasing amalgam concentration. The quantity of mercury distilled from each chamber should be continuously maintained under control. The condensation of the mercury vapors can be effected in coolers or heat exchangers which are located at the highest point of the plant. By this method,

a decrease in the quantity of circulating mercury and a simple return of the mercury to the cells may be achieved. The heat of condensation may expeditiously be employed for the production of steam. In this first distillation step there may be distilled off more than of the total mercury. As a consequence the greatest part of the total heat required is utilized in this step and, therefore, the efficiency of the process depends to a large extent upon the possibility of relying upon a cheap source of heat for this step.

The distillation apparatus for the second distillation step is preferably. a melting furnace constructed of ceramic material or pressed graphite and is operated without a reduction in pressure or with only a slight reduction in pressure.- The amalgam may be continuousl introduced into the furnace by a barometric overflow pipe, the pure zinc being taken off also'continuously by means of an overflow syphon filled with nitrogen. -It is possible to construct the meltin tion.

It is advantageous to conduct so much heat to the distillation unit that a quiet or even with large surface areas, to effect movement of the melt and to lead a rapid current of gas over the surface of the melt. For best results the heating in this unit should' be similar to that of the so-calledhigh frequency furnaces. Moreover, to avoid zinc deposits it is preferable to construct the condenser attached to the distilcury turbines, high pressure mercury 'vapor,

lation chamber according to the principle of the injection condenser and to operate it with the initial amalgam. We have also discovered that a considerable decrease in the size of the distillation plant can be achieved if the warm and well flowable zinc amalgam leaving the electrolytic cells is not subjected to distillation withvout further ado but is first cooled by allowing ed 'by decanting, sieving, centrifuging ,or the like.

The amalgam concentrate obtained in this 'way is advantageously further concentrated by mild pressing to a sandy, butter-like or loamy consistency. In this way there is obtained an amalgam having a zinc content of about 12%. The exhausted fraction which is returned to the cells is the poorer in zinc the lower it is cooled before fractionation. Y

The invention is illustrated by the accompanying drawings,

Fig. 1 of which discloses diagrammatically a plan view of a system according to the present invention, the cell being shown in section,

Fig. 2 a transverse section through the cell of Fig; 1, and

' Fig. 3 a flow sheet depicting'the steps followed according to a modification of the invention.

The invention will be further explained by reference to the following examples. It is to be understeod, however, that these examples are illustrative only.

Example 1 A zinc sulfate lye. containing about -105 iection condenser L which is loaded with the material while simultaneously neutralizing the sulphuric acid electrolytically formed. The readily ing molds. The mercury is recycled to the electrolytic cells. The zinc obtained has a purity of 99.98%.

' Example 2 The procedural steps followed according to this example are illustrated by Fig. 3 of the drawings.

Roasted pyrites of 55.10% Fe, 1.99% Cu, 2.39%-

Zn, 240 gms./ton Co, 300 gms./ton Mn, 0.04% Sb, 3.45% S, 0.11% As, 1.40% Pb, 4.05% SiOz, 62.0 gms./ton Ag; 1.02 gms./ton Au are, after addition of 10% sodium chloride, chlorinatingly roasted and lixiviated to produce a lye. The lye is de-coppered with iron clippings and cooled' to to efiect the removal of the bulk of the sodium sulfate. The remainder of the sulphur together with Fe, As, Sb, Mn and Co are precipitated by lime with simultaneous introduction of chlorine to a pH of 5.5. Alter filtration there is obtained a zinc chloride lye rich in sodium chloride, which contains magnesiumand calcium-chloride in small amounts. The zinc content amounts to 60 gms./liter. In the lyethere are still present per liter, 12 mg. Fe, 13 mg. Co, mg. Ni and some Pb as well as Cd. This lye is electrolyzed in cells designated on the drawing, as A which are similar to the cells used in alkali-chlorine electrolysis. The mercury cathode B is cycled inside the individual cells and flows in the form of a horizontal stream for a distance' of 8 millimeters under the graphite anode C with a speed of 9 cm./sec. The working temperature is 70 C., the current density 1200 amperes per square meter and the voltage of ab.

.32 v. Mercury is continuously introduced in each cell and amalgam with 44.5% zinc is continuously drawn oi! from each cell by an overflow E. The electrolyte F circulates through the cells in a continuous stream and leaves the cells with a content of about 20 grams of zinc per liter. The zinc is precipitated with lime and 80% at a temperature around 220 8% at a temperature around 260 5% at a temperature around 300 3% at a temperature around 350 The necessary heat is supplied to the distillation units by mercury vapor. The heat passes through the iron wall of the units which are protected by an enamel layer against the action of the hot amalgam. The concentrate obtained in this distillation step flows into an equalizing vessel R and from there into a distillation furnace I constructed of ceramic material. This furnace contains a zinc sludge maintained at a boiling temperature by high frequency heating. In this furnace the last residues of the mercury are evaporated and are precipitated together with the simultaneously developed zinc vapors in an ineach cell.

initial. amalgam. The mercury vapors from the first distillation are precipitated in heat exchangers M arranged at a highly elevated position in the system in which superheated steam is produced. The mercury condensate flows under the influence of gravity to the electrolytic cells. Zinc is obtained in a purity of 99.95%. The chlorine gas obtained is dried in the usual manner and condensed. In contradistinction to the chlorine gas obtained in the electrolysis of potassi chloride, it is free from hydrogem Example 3 A concentrate of zinc-lead-ore, which has been obtained by the flotation process, is mixed with a 24 fold quantity of roasted pyrites. The mixture then contains 57.90% Fe, 0.84% Cu, 3.57% Zn, 200 gmsJtonCo, l5 gins/ton Ni, 20 gms/ton Cd, 300 gms./ton Mn, 0.04% Sb, 0.09% As, 2.18%

Pb, 4.95% SiOa, 3.20% S, 49.0 gms./ton Ag, 1.26

gms./ton Au. It is mixed with 12% of sodium chloride and converted to a zinc lye in the manner described in Example 2. The lye is then subjected to cementation with zinc dust' to precipitate the metals more electro-positive than zinc. The lye now has a zinc content of 65 gms. per liter. The zinc is removed therefrom by a treatment in 4 electrolytic cells, lying one above the other so that the amalgam passes successively through the cells under the influence of gravity. The amalgam is moved in a cycle in The quantity of amalgam branched of! is so controlled that in. the first cell there is maintained an amalgam with a concentration volts. The current elllciency is -97%. BY

working up the amalgam according to the method 01 Example 2, zinc having a purity of 99.995% is obtained.

Example 4 Roasted Meggener pyrites is mixed with copper containing roasted pyrites in a proportion of 1:1. The mixture contains 53.00% Fe, 0.55% Cu. 5.20% Zn, 240 gms./ton Co, 750 gms./ton Mn. 0.04% Sb, 0.14% As, 0.53% Pb, 8.30% S102, 3.95% S, 25.00 gms./ton Ag, 0.82 gms./ton Au. Sodium chloride in an amount of 12% is added to the mixture and converted into azinc lye containing 65 grams of zinc per liter according-to the meth- 0d of Example 2. The lye obtained is electrolyzed at a temperature of about 75 C. with a current density of 800 amperes per square meter and a voltage of about 3.1 volts in four electro lytic cells while operating as described in Example 3. An amalgam containing 4.35% of zinc is produced in the electrolysis. The amalgam is cooled to 5 C. by allowing it to flow into airfree cold water containing 0.5 gram of HCl per liter, and is separated by means of a helical sieve into 56 parts of a readily flowable fraction containing 1.65% of zinc and into 44 parts of a doughy concentrate containing 7.80% of zinc. The concentrate is continuously forced by means of a conveyorpress into the distillation apparatus. By distillation 40.6 parts of mercury are obtained whereas, had the amalgam been distilled without mechanical concentration, it would have been necessary to have distilled of! 75.4 parts of mercury. The distillate is combined with the afore-mentioned readily flowabie fraction to produce an amalgam containing 1% of zinc which is then returned to the electrolytic cells. The,last traces of mercury are removed from the zinc by heating in a graphite furnace brought to 900 C. by Kryptor' heating (a form of resistance heating wherein the resistance element is made from a mixture of graphite, carborundum and the like) 99.96% is obtained.

Example 5 A zinc amalgam obtained by electrolysis according. to Example 4 is cooled to 18 C. by al-. lowing it to flow into 0.01 n hydrochloric acid. Byleading the amalgam over a shaking screen and mildly pressing it, there are obtained 21.5 parts of concentrate containing 12.2% of zinc and 78.5 parts of a fraction containing 2.2% of zinc. The subsequent distillation of the concentrate results in the production of 18.9 parts of v mercury whereas, had the amalgam been directly distilled without previous concentration, the distillation would have led to the production of 57.6

parts of mercury. The concentration prior to distillation, therefore, results in a 66% saving in the distillation. I

' Example 6 Example '7 The trough or channel serving for the circulation of the amalgam in a cell is provided with an air-tight closure and is sealed at its ends by means of plates immersed in the amalgam to such an extent that, while the amalgam may still i flow in the trough, the plates operate to close 01! the whole transverse section of the trou h which is not occupied by amalgam. In other words,

said end plates, while immersed in the amalgam,

' do not extend to the bottom or door of the channel or trough. Water at a temperature of about 70 C. and containing 3.5 gms. per liter of HCl trickles over the surface of the amalgam inside of the trough. This provides an alternative method for insuring that oxygen will not be permitted to contact the amalgam, thereby preventing the formation of slag in the amalgam.

Example 8 A zinc-chloride lye containing sodium chloride, .03 gram per liter of arsenic and .04 gram per liter of antimony, has added thereto an excess of ferric chloride. The iron is then precipitated by A zinc having a purity of I phragm, and circulating the amalgam in horizontal rows or streams whiie avoiding turbulence and insuring uniform motion, the amalgam being circulated at such a slow rate of speed that no isolated deposits of high zinc concentration occur.

2. Process for the production .of zinc from zinccontaining lyes which comprises electrolytically depositing zinc continuously from said lyes at a.

temperature in excess of 55 C. in a plurality of electrolytic cells into a mercury cathode which electrolysis is eflected without the use of a. diaphragm, causing the mercury to circulate through said cells and controllingthe degree of zinc deposi the addition of lime. The lye thus obtained is cathode ata current density of 1500 amperes per square meter and a voltage of ab. 3.4 volts while operating according to Example 3; The zinc amalgam thus obtained is then worked up into zinc and mercury in the manner previously described.

tion in each cell so that the mercury cathode gis enriched by degrees in zinc to produce a readily flowable amalgam. x Y

3. Process for the production of zinc from zinccontaining lyes which comprises electrolytically depositing zinc from said lyes .into a. mercury cathode cooling the amalgam by causing it to flow into cold, weakly acidified water, mechanically working the amalgam thus obtained to produce a concentrate high in zinc and a fraction low in zinc, mixing fresh mercury with the fraction low in zinc and using the resulting mixture as the cathode.

4. Process for the production of zinc from concentrated zinc-containing solutions which comprises electrolytically'depositing zinc, from said solutions without the use of adiaphragm at a temperature in excess of C. into a mercury cathode to form a readily flowable amalgam and discontinuing the electrolysis of said solutions when the zinc concentration falls to from 15 to 20 grams per liter.

5. The process asdefined in claim 4 wherein a I lye is electrolysed containing besides -zinc other metallic constituents and which lye has been freed from arsenic and antimony.

6. The process as defined in claim 4 wherein a lye is electrolysed containing besides zinc other metallic constituents.

'7. Process for the production of zinc from concentrated solutions. containing zinc which coniprises electrolytically precipitating the zinc from these solutions without the use of a diaphragm at a temperature above 55 C. to produoea readily flowable amalgam, and at a current-strength selected that the surface of the amalgam remains bright and undisturbed and discontinuing the electrolysis when the concentration of said solutions has decreased to 15 to '20 grams per liter. 

